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We analysed with multigene (18S and COI) metabarcoding the effects of the proliferation of invasive seaweeds on rocky littoral communities in two Spanish Marine Protected Areas. The invasive algae studied were Caulerpa cylindracea , Lophocladia lallemandii and Asparagopsis armata . They are canopy-forming, landscape-dominant seaweeds, and we were interested in their effects on the underlying communities of meiobenthos and macrobenthos, separated in two size fractions through sieving. A new semiquantitative treatment of metabarcoding data is introduced. The results for both markers showed that the presence of the invasive seaweed had a significant effect on the understory communities for Lophocladia lallemandii and Asparagopsis armata but not for Caulerpa cylindracea . Likewise, changes in MOTU richness and diversity with invasion status varied in magnitude and direction depending on the alga considered. Our results showed that metabarcoding allows monitoring of the less conspicuous, but not least important, effects of the presence of dominant invasive seaweeds. [ABSTRACT FROM AUTHOR]

• Metabarcoding confirms broad, generalist diet for C. crangon and C. maenas. • Clear niche separation was detected, notwithstanding a high overlap in prey items. • More spatial variation in shrimp vs. crab diet; finer reflection of local diversity. • Trophic metabarcoding enhances the re-evaluation of estuarine interactions. • Diet assessment of sentinel species can reveal novel insights in marine networks. Epibenthic predators in estuarine shallow soft-bottom environments are generally considered to have broad ecological niches with a wide overlap. This allows them to cope with abundant but highly variable prey communities. The assessment of trophic relationships in shallow soft-bottom habitats is, however, challenging and often complicated by the bias and low resolution of the analytical tools available to study diet in relatively small invertebrates. This study investigates niche overlap between two dominant epibenthic predators in European estuarine soft-bottom environments, the brown shrimp (Crangon crangon L.) and the European green crab (Carcinus maenas L.), by means of trophic DNA-metabarcoding with universal primers for cytochrome c oxidase I (COI). Results show differences in diet composition between the two predators, despite the fact that both species are opportunistic generalists with a high overlap in prey items (218 overlapping Molecular Taxonomic Units). The European green crab showed a richer, more even, and more geographically consistent diet than the brown shrimp, with fairly balanced consumption of algal, arthropod, annelid and mollusc food items. The brown shrimp instead preferred arthropods and annelids, and showed more spatial variation in diet. The observed niche separation could be linked to behavioural variation between the two predators, with European green crab showing more active movements over shallow soft-bottom environments compared to the brown shrimp, which regularly stays buried in the sediment, ambushing its prey. An accurate understanding of the trophic ecology of these estuarine crustaceans is important to capitalise on their role as sentinel organisms since their diet reflects local diversity and can result in toxin bioaccumulation. This study provides new insights in the predator–prey relationships and food web dynamics in European estuaries and highlights the importance of trophic DNA-metabarcoding to study marine food webs. [ABSTRACT FROM AUTHOR]

We face an increasing global food security challenge as the human population continues to grow across the globe. As agricultural production rises to keep up with food demand, so too does the expansion of crop detrimental pest species. Early detection can be crucial to control their damage and relies on the use of accurate and dependable techniques. We report the first record of rice water weevil (Lissorhoptrus oryzophilus) in the Iberian Peninsula. The distribution range expansion of this invasive rice pest weevil is confirmed through traditional sampling and through natural sampling by bats combined with DNA metabarcoding, a non-invasive technique with strong potential for early detection of pests in agricultural areas. Presence of rice water weevil was confirmed genetically from bat faecal samples collected from a Pipistrellus pygmaeus bat roost in the Ebro Delta (Catalonia, Spain). The known distribution of this rice pest, native to North America, now includes four of the top five rice-producing European countries. To date, the economic damage caused by this pest in Europe is minimal and concentrated in small areas, but chemical and agronomic controls are implemented to control their populations. The nature of this record highlights the potential of insectivorous bats as natural samplers to detect (and possibly control) pest species in crops. Further studies are required to determine the full extent of the rice water weevil's spread, and to investigate integrated pest management systems, including biological control to suppress their populations. • Insectivorous bats consume a large diversity of detrimental crop pests. • DNA metabarcoding of bat faeces provides a powerful natural sampling tool. • This non-invasive technique can provide important early detection warnings of pests. • With this method, we confirm the first record of the rice water weevil pest in Spain. • This invasive weevil is now in four of the top five rice producing European countries. [ABSTRACT FROM AUTHOR]

• Environmental (eDNA) metabarcoding was compared to fishing in three estuaries. • eDNA generally detected a greater fish species richness than fishing. • eDNA could discriminate different fish assemblages between summer and autumn. • eDNA could detect fish assemblages between different estuaries. • eDNA can efficiently assess fish biodiversity in estuaries. Estuarine ecosystems are threatened by numerous anthropogenic pressures. Fish assemblages are a dominant component of estuarine macrofauna and serve as indicators for the health of these transitional water ecosystems. Environmental DNA (eDNA) metabarcoding is increasingly used to assess the biodiversity of fishes in estuaries. However, there is a need to further establish how effective eDNA metabarcoding can be relative to conventional fish sampling methods across multiple estuaries and seasons. This study compared fish assemblages detected via eDNA metabarcoding of surface water samples to contemporary sampling with conventional fishing gears in three temperate estuaries (UK), during early summer and autumn. Most species caught by fishing were detected by eDNA. Species richness estimates from eDNA were two to ten times higher than estimates based on fishing, and included taxa of conservation importance and a non-native species. The eDNA assemblage composition was significantly different to the assemblage detected by seine nets. Importantly, eDNA methods could effectively discriminate between fish assemblages of different estuaries and seasons. Fish assemblages in estuaries are often not monitored due to resource constraints. The dynamic nature of estuaries may make fishing gear deployment difficult and inconsistent. The findings indicate that eDNA metabarcoding is suited to gathering large amounts of information on fish biodiversity, at a relatively low sampling effort, compared to established fishing methods. Therefore, eDNA shows promise as an assessment tool for fish assemblage structure and ecosystem health in estuarine environments, with application to statutory monitoring. [ABSTRACT FROM AUTHOR]

• Combining eDNA and trawl data increases the detected biodiversity. • Good reference databases are of vital importance for correct taxonomic classification. • We advocate that a combined sampling effort is a good strategy for future monitoring of biodiversity in the Arctic including the Barents Sea. Managing natural resources in a sustainable manner requires understanding the complexity of ecosystems and the species that are associated with the different parts of the ecosystem. Much of this knowledge is derived from traditional sampling methods (e.g., different types of trawls). The analysis of environmental DNA (eDNA) can provide increased knowledge, complementary to the traditional methods. In the present pilot study, we sampled eDNA from two geographical areas, north and west of Svalbard (NWS) and in the southwestern Barents Sea (SWBS). The combination of trawling, visual identification of mammals and eDNA collection facilitated a robust analysis of fish and marine mammal diversity and species composition. Through 12S MiFish metabarcoding of the eDNA samples, we found that incorporating eDNA data provided an additional level of information on both the diversity of fish and marine mammals in the study areas. By adding eDNA data to the trawl data, we found that richness increased from 32 to 49 fish taxa. Significant differences in diversity and composition of the fish communities were detected by eDNA between the two study areas. Considering degradation and dilution factors it is postulated that the results represent resident species to the Barents Sea and that long -transported DNA from other areas are less likely. [ABSTRACT FROM AUTHOR]